This invention relates generally to (a) a dunnage material, (b) preparation of such dunnage material and (c) use of such dunnage material.
Dunnage materials such as foamed plastic particles or strands are known to be highly desirable for use in packaging articles. The foamed particles or strands protect articles in shipping by absorbing shock and by isolation of the articles from shipping container walls. Typical particles or strands are set forth in U.S. Pat. Nos. 3,188,264 and 3,723,240.
Dunnage materials are usually placed beneath, around the sides of, and atop articles being packaged in order to isolate the articles from container walls. Packaging relatively light articles in this manner is generally effective. Packaging delicate but relatively heavy articles, such as electronic or optical equipment, in this manner is less effective.
It has been found that relatively heavy articles tend to "migrate", or move through, the dunnage materials due to vibration or handling. For example, in shipments in a truck, van, or rail car, migration of these heavy articles frequently continues until contact is made with a shipping container wall and breakage or other damage occurs. Breakage from this and other causes may be as much as fifteen percent, or even higher, especially where prolonged shipment or handling is involved.
A number of attempts have been made to reduce migration through dunnage materials.
Holden, in U.S. Pat. No. 3,188,264, discloses particles having a number surface indentations to promote interlocking between particles.
Skochdopole et al., in U.S. Pat. No. 3,723,240, discloses asymmetrically foamable strands which curl upon foaming to form a generally helical structure. The helical structures interlock to a degree when placed under pressure.
Humbert et al., in U.S. Pat. No. 3,251,728, disclose a dunnage material consisting essentially of a tangled interlocking mass of non-linear, elongated pieces of foamed polymer.
Graham, in U.S. Pat. No. 3,047,136, discloses a dunnage material which consists of a plurality of strings of hollow crushable cylinders, each of the strings being partially cut through at spaced intervals. A resilient or rubbery outer coating may be applied to the strings to reduce sliding of the strings relative to each other as well as to supplement interlocking between the strings.